Portion of a light bulb



FIG. 1 is a bottom, right perspective view of a portion of a light bulb showing the new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a left-side elevational view thereof;

FIG. 5 is a right-side elevational view thereof;

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom plan view thereof.

The broken lines in the figures depict environmental subject matter and form no part of the claimed design. 

CLAIM The ornamental design for a portion of a light bulb, as shown and described. 